Field of the Invention
One disclosed aspect of the embodiments relates to a photoelectric conversion apparatus and an image capturing system. In particular, an embodiment relates to a photoelectric conversion apparatus and an image capturing system provided with an AD converter.
Description of the Related Art
An image capturing apparatus provided with an AD converter has been proposed.
Japanese Patent Laid-Open No. 2009-177797 discloses AD conversion of a ramp-based approximation method in which a reference signal of which signal level changes with time and an analog signal are compared to obtain a digital signal. It is also disclosed that changing a rate of change of the reference signal with time may change a gain in AD conversion.
In Japanese Patent Laid-Open No. 2010-045789 discloses an image sensor that compares an analog signal with a threshold obtained by dividing an amplitude of a full-scale analog signal by 2k. In this related art, if an analog signal is larger than a threshold, the analog signal is compared with a reference signal having a relatively large rate of change to obtain n-bit digital data on the MSB side.
If the analog signal is equal to or smaller than the threshold, the analog signal is compared with a reference signal having a relatively small rate of change to obtain n-bit digital data on the LSB side.